Usually, a radial tire is provided with a belt reinforcement comprising a breaker A and a band B, wherein the band cords are generally laid in parallel with the circumferential direction of the tire, and on the other hand, the breaker cords are inclined with respect to the circumferential direction. Such belt reinforcements are shown in FIGS. 9-11. FIG. 9 shows a full band B composed of a full width ply. FIG. 10 shows an edge band B composed of a pair of edge plies. FIG. 11 shows a combination band B composed of a full width ply b1 and a pair of edge plies b2.
The edge plies are effective for increasing the hooping force at the breaker edges, and accordingly effective for preventing ply edge looseness and separation.
Usually, such a band ply is formed by winding a ply material having the same width as its finishing width, around the carcass, and the ends of the ply are overlapped each other at a certain length as shown in FIG. 12. Accordingly, the thickness and rigidity are increased at the joint J, and RRO (Radial Runout) is increased, and further, the tire uniformity is disturbed.
In order to solve those problems a jointless band may be used, but as shown in FIG. 16, to form an edge ply at each edge of a breaker, when a strip T is wound separately at each breaker edge, since the number of the windings or turns in each ply is small and the both ends of the strip are free, the wound strip is liable to be loosened and shifted during a tire vulcanizing process by the increased cord tension, and accordingly the ply has an uneven thickness distribution to increase RRO, and the tire uniformity is disturbed.
On the other hand, various types of jointless bands have been proposed.
In order to form a band like the above-mentioned full width band B in FIG. 9, Japanese Utility-Model Publication (JITSUYO-KOKAI) No. 61-15604 discloses a band B shown in FIG. 13, wherein a strip T is wound spirally at regular pitches from one edge to the other edge of a breaker, while slightly overlapping the adjacent edges thereof. Accordingly, the hoop effect is not enhanced at the breaker edge regions at which a strong hooping force is required.
In Japanese Patent Publication (KOKAI) No. 62-203803, a band B having a double layered structure at the edge of a breaker A like the band B shown in FIG. 11 is disclosed, wherein a strip T including reinforcing cords of 1 to 8 in number is wound, while traversing a breaker A as shown in FIG. 14. However, the traversing direction is changed at least twice as indicated by an arrow to wind the strip around the previously wound portion thereof. Therefore, it becomes hard for the band to obtain a dimensional accuracy and a positional accuracy, and further the productivity is lowered.
Further, the allowed Japanese Patent Publication (KOUKOKU) No. 1-278803 discloses a band B also formed by winding a strip T around a breaker A, wherein the strip is overlapped as shown in FIG. 15. In a central region, the overlap is 50% of the strip width and the overlap is increased to 75% in side regions. Accordingly, the band has a double layered structure even in the central region, which results in an excessive increase in the hooping force in the central region as well as a decrease in cornering power. Further, the tire weight increases.